1. Field of the Invention
The present invention relates to a copy prevention method and apparatus of a digital .[.magnetic.]. recording/reproducing system, and more particularly to a copy prevention method and apparatus of a digital .[.magnetic.]. recording/reproducing system, wherein a marker involving copy prevention function information and executing the function is coded and inserted to perform the copy prevention function and realize the copy prevention function of various patterns desired by a program supplier.
2. Description of the Prior Art
One example of a conventional copy prevention method is described in U.S. Pat. No. 4,819,098, in which a signal inducing an interference to an automatic gain controller (AGC) circuit within a VCR is inserted to a video waveform to be recorded on a tape. When the tape is reproduced to display the signal on a television, the interference signal does not affect the AGC circuit of the television .[.to allow.]. .Iadd., allowing .Iaddend.for a normal display.
However, when the reproduced signal is recorded by another VCR, i.e., when it is duplicated, the interference signal brings about .[.the.]. interference in the AGC circuit of the .Iadd.recording .Iaddend.VCR .[.to record in.]. .Iadd.causing .Iaddend.an inaccurate signal level .Iadd.to be recorded.Iaddend.. Accordingly, the nodal display cannot be attained when reproducing a duplicated tape.
As another example, U.S. Pat. No. 4,571,642 utilizes a control track employed during performing the reproduction for synchronizing a servo circuit within a VCR, .[.thereby.]. .Iadd.for .Iaddend.embodying the copy prevention function. The basic concept of this patent is for altering a video signal to force the control track to be inaccurately recorded when the video signal is duplicated onto another tape.
Still another example is disclosed in U.S. Pat. No. 4,577,216, in which a phase noise or the like is inserted .[.to.]. .Iadd.in .Iaddend.a chroma burst portion of a video signal to thereby embody the copy prevention function.
The above-mentioned methods .[.are for using.]. .Iadd.using .Iaddend.a difference .[.of.]. .Iadd.between the .Iaddend.sensitivity .[.between.]. .Iadd.of .Iaddend.circuits .[.of.]. .Iadd.in .Iaddend.a television and .[.of.]. a VCR. .[.Thus, the copy prepared to prevent the copy thereof as above may not exert the copy prevention function in a certain VCR, but may not execute a normal display on a certain television..].
The above copy prevention methods are of an analog system, which are available for preventing the copy of an NTSC-class video signal to an analog VCR. However, in case of a high-definition image of the analog television (ATV), the copy is performed by means of a digital VCR rather than an analog VCR, so that it is difficult to employ the copy prevention method of the analog system.